1. Field of the Invention
The present invention relates to an apparatus for feeding multi-phase AC current from a DC power source and a rotating field apparatus having the AC feeding apparatus.
2. Description of the Prior Art
Various types of inverter feeding apparatus have been used. For example, three phase bridge inverters have been used for multi-phase AC feeding to rotary machines generating the rotating field. The three phase bridge inverters have been especially used for an internal electromotive force solid commutation motor with a synchronous motor.
For example, various motor apparatus combining a solid-state AC feeding apparatus with an AC motor such as non-commutator motors, thyristor motors and inverter feeding induction motors, have been known. These apparatuses are solid commutator motor having solid switch elements as a commutator. The combinations of a current source type converter with a synchronous motor or an induction motor impart excellent driving and regenerative braking in economical operation and they are called as "non-commutator motor" or "current type variable frequency inverter".
FIGS. 1(a), (b) show connections of a solid commutator motor having the conventional inverter wherein the references P and N are respectively designate DC input terminals; (4) designates a smoothing reactor; (300) designates a solid commutator (inverter) in a bridge connection; (100) designates AC windings for an AC motor.
FIG. 1(a) shows a three phase type embodiment and FIG. 1(b) shows a six phase type embodiment. The AC windings of the conventional AC motor are in three phases or six phases. Accordingly, the solid commutator (300) is the three phase bridge or the six phase bridge of solid switches. The apparatus having the three phase AC windings and three phase bridge shown in FIG. 1(a) has been especially used.
However, the AC windings have internal connections shown in FIG. 1(c) wherein pairs of windings (U, U), (V, V), (W, W) in the reverse phase are respectively connected to form the phases. As the appearance, they have three phases however the structure is the six phase structure.
FIG. 1(d) shows the space distributed regions of sectional view of the conductors for the windings. In the conductor distributed region for one phase, six groups of the coil groups U, V, W, U, V and W for an electrical angle of .pi./3 are used and the return conductor distributed region U', V', W', U', V' and W' is used. The coil pitches of the coils are usually short pitches. In the short pitches, the return conductor is not disposed to the position shifted for an electrical angle of .pi..
Thus, the three phase connection of FIG. 1(a) provides the six phase winding structure for a motor whereby the winding operation is the same with that of the six phase connection of FIG. 1(b).
The solid commutator (300) commutate for 6 times per one cycle in the embodiment of FIG. 1(a).
In the embodiment of FIG. 1(b), one of the positive solid switches (3ap) to (3fp) and one of the negative solid switches (3aN) to (3fN) such as (3ap) and (3dN) are simultaneously turn-on in the turn-on control. Each pair of the AC windings U and U; and V and V; W and W are simultaneously commutated. Thus, in the six phase connection, the solid commutator commutates for 6 times per one cycle.
The characteristics of the motor and the structure of the windings are substantially the same in the embodiments of FIGS. 1(a) and (b). The embodiment having six phases has no advantage for double of phases. The conventional solid commutator motor has small series connections of the solid switches whereby it is difficult to apply high voltage. The solid switches are mainly connected in parallel whereby it is difficult to mount them in one piece.
In the bridge type inverter, the pulsation caused by switching is large and the arrangement of connections of the solid switches is complicated disadvantageously.
The conventional apparatuses have disadvantages of the large switching pulsation and the complicated arrangement of the solid switches.